Conventional air washers introduce a constant amount of water spray into the air washer chamber to saturate the air supply leaving the air washer to approximately 95% relative humidity. Even with air washer bypass, heat is required when the sensible heat gain in the conditioned area drops below approximately 67% of its design heat load. Even when chill water is introduced on a separate bank of sprays or manifold together with recirculating water (see U.S. Pat. Nos. 3,965,690, 4,604,108 and 5,247,809), these conventional air washers still saturate the air supply to a fixed relative humidity, provide no means for throttling the recirculated water sprays to obtain a variable discharge relative humidity, and require heat to maintain desired conditions in a partially loaded space.
Air washers incorporating spray throttling techniques, such as those described in U.S. Pat. Nos. 4,089,666, 4,312,189 and 4,399,864, introduce chill water into the suction side of the recirculating water pump. During light load periods this requires minimum recirculating water sprays to maintain the desired psychometric conditions in the conditioned space. This in turn can produce an overcooling effect and require heat to maintain the desired space psychometric conditions. During periods when a substantial amount of outside air is required to maintain the desired air washer discharge dew point temperature and the outside air is humid, the air supply is saturated to a higher relative humidity than is desired and heat is required to dry it out.
Another problem that occurs when conventional or spray throttling air washers are connected to one chill water supply system is that during the winter months the chill water is turned off and each washer must operate independently. This means that a central chemical water treatment system does not function during this period. Automatic chemical feed systems installed on individual air washers are expensive. Owners often resort to manually feeding chemicals into each air washer which produces overfeeds or underfeeds and less than optimum results. Also the chill water piping interior is exposed to air and corrodes more during this period.
Conventional air washer controls with or without spray throttling capabilities utilize space temperature control to maintain the desired psychometric conditions in the conditioned space. In some instances, high limit humidistats are provided to override the space thermostats in the event that chill water is unavailable when it is needed. This does not provide consistent control of conditioned space relative humidity when chilled water is required but unavailable. It also uses more energy than necessary.
Air washers are used to condition spaces where precise psychometric conditions are required and where the internal sensible heat gain is usually much higher than the external heat gain. In most cases latent heat gain or loss in these spaces is negligible when compared with the sensible heat. However, there are several cases where this is not true. For example, when water jet looms are used in the textile industry, there is a large latent heat gain in the space that is uncontrollable. In northern climates during the winter time, where outside walls have inadequate vapor barriers there are large latent heat losses.
Traditional spray throttling air washer control systems compensate for space latent heat load changes by increasing or decreasing the recirculating water spray saturation. This provides overcooling or undercooling, poor control, and excessive use of heat.